Separation of methyl amines



Patented Apr. 3, 1951 I TED S T 10 ICE '2;547,o`64 snrAitrlrroiv or METHYL AMI-Nus William Tyerman', Norton-on-'eealEngland,,as-

:signor to, Imperial Chemical .Indu's'trlies Limited, a corporation of Great Britain No. 788,081. 2e, 1294,16

Thisfinvention relates to methods ci' sepa-rating 5organic nitrogen compounds. u u u y According to the present invention 'monom'eth- .'yla'rnirre is separated as vapour from "mixtures containing it and one or both -of the other methyl amines by Aselective absorption of -thef'other amine 6r amines by 'an-organic yliquid selected "from the group: alkyl substituted anilines; alicyclic amines; lower aralkyl ethere; quinoline; vthe nitro-derivatives "of aroma-tic hydrocarbons; h-ydrogenated naphthalenes; higher alkyl ben'Ze'nes; terlp'en'es; and t"chloriirated aromatic hydrocar- "-bonfsil 'The preferred form vof the present lprocess is vex'traetiv'e vdistill'tion as hereinafter rdened.

By v"selec'stive absorption in this specfic'ati'on isfmeant ra A'process for 'separating onejor more substances from a rnxture containing two for 'more substances ii'r'hi'ch comprises: treating lthe mixture, which may be in "liquid or vapour ffo'rm, 'in -bountei 'current with an extracting liquid Vso *as to obtain at least one 'of the vsubstances 'as vapour and selectively absorb 'one .or rnore Vof them in the liquid; 'and takingfoff one or more oi them l"asifapour ata fp t .in the system fabove or fb'ey'h'd the point of iv oduction rof the `mixture. Preferably the L'pr'ocess 'i's conducted in a cirhiito Aune mixturezis fed :and .in which the treatment "is -eiectd the mixture, preferably, being fed to the bottom =of the column, -t'he lexrtracting liquid being fed at a point above this Vand 'the vapour being taken off 'from the top of the `ieolu'mn.

By textr'activedistillation `in this speciiieation is meat I'a process-of selective 'absorption which vv"cted in a columnjan'd Ais characterised by the features that the mixture to be treated is fed to the 'column at an vintermediate point 'in the column, the extracting liquid is lfe'd lat a 4point above this, preferably at ith'e top 'of the 'column the vapour is taken oli from the top of the 'fe'olum'n an'dfat least "some of the more soluble substance l'or 'substances absorbed in the 4liquid is desol'bed Vfrom the liquid at the rl'io'tttrn Of "the column or outside the "column, and is again brought in fcontaot with the extracting liquid at, or in the neighborhood of, the bottom of the column. This 'may be achieved, Ifor example, by employing a boiler at the bottom voi the column, and returning said substance or 7'substances to the column-as vapour, or/by )removing the extracting liquid from the bottom of the column, strip- Jping lfrom Iit the more soluble substance "orsubstances 'in a separate still, and returning the 'des'ifre'd proportion of said substance or v'subfsta'nces to the 'bottom "of 'the 'column as reux. i The proportion of the more soluble substance or substances 7returned, as refluxkwill depend on the purity desired in the'product, and on the relative solubilities of the individuals to befseparated.

In Great Britain November 4'o1aim's. (c1. 'abasaisi 1 'diirerence iin solubility of the substancesv in the extracting liquid is small a high proportion of 4rd'f-isorbed vapour will .be returned as redux. n In Ipractice the proportion 'to be absorbed as 4reiiux ican be readily determined by those skilled lin the art. u l

In ia'll these processes vit Tis preferable 'that the extracting :liquid should have a boiling point at the operating pressure at least 50 C. vhigher than vthe boiling point `of Ithe most soluble-'substance in order that the last mentioned may be readily separated .from the lliquid by distillation.

In all these processes, also; 'the mixture may Ibe fed 'to the system asl-vapour or as liquid, in Whiehflast case the vaporisation takes .place Within 'the system', that is within the Ycolumn when `a column is used. u

The process of extractive distillation of the present invention may befdirected to the preparation of Vsubstantially .pure monomethylamine, in which case it will be operated so that not all of the monomethylamine is expelled from the extracting liquid, or it may be directed to the prepvaration` of one of the other amines, or of a mixture or these, substantially free from monomethylamine, Vin Which case it will be operated so thatI vthe monomethylamine separated as vapour contains respectively one or both of the other amines. Both these procedures are in- 'eluded within the scope of the invention but the former lis considered to bethemore important of the two. vThe other amine or mixture of amines may be subsequently recovered from the extracting liquid by stripping.

Furthermore, when the mixture being treated contains the three amines, and the liquid is one in which the dimethylamine is less soluble than the trimethylamine, or vice versa, the process .maybe employed `for the separation (asvapour) of a mixture oi monom'ethyla'mih'e 'and the other levasftslble famine irom the most soluble amine, v rhichremains in solution inthe extracting liquid. This is of particular importance Where the Ymost solublearnine is the desired product. AThe desired .amine .can subsequently be recovered from its solution by distillation. The mixed amines taken on :as vapour may b'e returned to the amination unit, or-may, .ifrdesir'ed be separated by fractional vdistillafi'fiofn or selective absorption, in particular fby -extra'ctfive .distillation The yinvention is to be considered as including the Amethod of operation described in this paragraph but does not include the ,fpro'cess clainfied in applicants copending UnitedStatesapplication, Serial No. 788,082, filed .November 25., T1947.

The .process very valuable for separating -inonomethylamine lfrom mixtures of the amines alsocontainingammonia .Infsueh case it is preferredto remove the ammonia prior to the process of the present invention, However, if desired,

most organic solvents, e. g. are: aniline, the lower v alkyl anilines, the mono-amines of the alkyl benzenes, the aliphatic mono-alcohols,icyclicmonfr-V alcohols, mono-nitro derivatives of benzene andY of the alkyl benzenes, hydrocarbons, chlor-substituted cyclic hydrocarbons and the fOrmamides. A When the ammonia is to be removed in a. separate stage prior to the separation of monomethylamine by the process of the present invention this may be done by selective absorption or by extrative distillation 'with one offthe last mentioned liquids.

In particular there may be employed in the process of the present invention one of the folmethylamine is less than that of the other methylamines, and for which the ratio, solubility of monomethylamine: solubility of next least Hsoluble methylamine, measured as`litres of gas per 1GO mls. of liquid at 20 C., is not more than 0.71:? dimethylaniline; monoethylaniline; diethylaniline; dimethylcyclohexylamine; quinoline; nitrobenzene; o-nitrotoluene; tetrahydronaphthalene; decahydronaphthalene; cymene; pinene; cedrene; o dichlorbenzene; a chlornaphthalene. f The solubilities of the three methylamines in these liquids at C. are given in the table below.

liable Solubility: litres of gas/100 mls. of liquid ai; 20 C.

Liquid mrlll. dimcthylatrimethylamine mine mmc Dme'thymniline-- c. 4 2a. o 14. 9 monocthylaniliue. ll. 3 32. 4 22. 8 diethylanilina 0 1S. 0 13. 4 dixuethylcyclohcxylamiue (i. 7 18. 7 18. 7 quinoline 9. 2 21.2 25. 5 anisole 8. 9 25. 2 1S. 5 nitrobenzcnc. 8. 8 22. 6 15. 4 onitrotoluenc 8. 6 22. 1 14. 9 tctrahydronaphtbalene 4.0 17.0 15. 1 dccahydroimphthalene 2. 4 1l. 6 15. 0 cymene 4. 8 18. 2 17. 7 pinenc 3. 4 15.5 17. 6 ccflrcne 3. 4 10. 6 8. 6 o-fliohlorbenzene... (i. 4 25. 2 24. 0 ,zx-chlornaphthalcn 5.2 V17.4 13.0

The preferred extractive liquids are: dimethylylcyclohexylamine, quinoline, tetrahydronaphthalene, decahydronaphthalene, cymene, pinene, o-dichlorbenzene, alpha-chlornaphthalene, and anisole. Y f

It is convenient to employ these liquids for the separation of monomethylamine as vapour atA temperatures in the neighbourhood of 20 C., but temperatures of from about 8 C., up to about 40 C. may be employed if desired. Most frequently lowing liquids, in which the solubility of mono- 20 aniline, monoethylaniline, diethylaniline, dimeth- 5 to include in the system a 'presaturator of the type vdescribed in co-pending British application No.

35,879/46, 4applied i`or .by A W; Tyerman and F. Wrigley, filed on December 4, 1946, and issued as British Patent 630,884. The monomethylamine is obtained as vapour from the top of the column while the diand/or tri-methylamine are obtained from'the bottom of the column as a solution in the extracting liquid. The vapour, which may comprise one-or more of the other methylamines is expelled from this solution by heating,

a portion isreturned to the bottom of the column as reflux and the remainder is taken to storage. The' extracting liquid stripped from amines is cooled and returned tozthe pre-saturator.

Simple selective absorptionas applied to -lthe separation of monomethyl'amine .from a mixture of the three methylamines may be conducted, for vexample, by scrubbing the mixture counter-currently in a column. with one of the aforesaid liquids, taking ofi substantially pure monomethylarnine from the top of the column and a solution of the three amines from the bottom of the column. The feed is introduced at the bottom of the column and no rei-ux is used.

I claim:

l. A process for the separation of monomethylamine from its admixtures from other methylamines, which comprises selectively absorbing at least one of the other methylamines together with at least some monomethylamine by a liquid as hereinafter defined, removing substantially pure monomethylamine as a vapor at a, temperature Within the range of 8 to 40 C., said liquid being an organic cyclic hydrocarbon derivative having a boiling point at the operating pressure at from the group consisting of tetrahydronaphthalene, cymene, pinene, cedrene, o-dichlorobenzene, alpha-chlornaphthalenel and decahydronaphthalene. f

' 2. A process for the separation of monomethylamine as set forth in claim 1, wherein a pressure.

of up to 20 atmospheres gauge is employed.

3. A process for the separation of monomethylamine as set forth in claim 1, wherein said selectively absorbed methylamines are recovered from the extracting liquid by Stripping, the said stripped liquid being returnedv to the system for further extraction. n fy.

4. A process for the sepa-ration of monomethylamine as set forth in claim l, wherein a portion atmospheric pressure will be employed, but pressures above or below atmospheric may also be" used. If superatmospheric pressure is used a suitable range is up to 20 atmospheres gauge.

The extractive distillation may be carried out employing columns of known type, e. g. packed, sieve-plate or bubble cap columns. Preferably the mixture containing the methylamines is introduced at an intermediate point in the column, most conveniently in vapour form. It is preferred o'f' said monomethylamine obtained as a vaporis returned-to the system asreflux, the remainder being utilized as product.

WILLIAM TYERMAN.A

` RErEENoas siren. The following references are of Vrecord in OTHER REFERENCES Herold et al.: 36 Chemical Abstracts 786. i 

1. A PROCESS FOR THE SEPARATION OF MONOMETHYLAMINE FROM ITS ADMIXTURES FROM OTHER METHYLAMINES, WHICH COMPRISES SELECTIVELY ABSORBING AT LEAST ONE OF THE OTHER METHYLAMINES TOGETHER WITH AT LEAST SOME MONOMETHYLAMINE BY A LIQUID AS HEREINAFTER DEFINED, REMOVING SUBSTANTIALLY PURE MONOMETHYLAMINE AS A VAPOR AT A TEMPERATURE WITHIN THE RANGE OF 8* TO 40* C., SAID LIQUID BEING AN ORGANIC CYCLIC HYDROCARBON DERIVATIVE HAVING A BOILING POINT AT THE OPERATING PRESSURE AT LEAST 50* C. HIGHER THAN THE BOILING POINT OF MONOMETHYLAMINE, CHARACTERIZED BY THE FEATURE THAT THE RATIO OF THE SOLUBILITY OF MONOMETHYLAMINE TO THAT OF THE NEXT LEAST SOLUBLE METHYLAMINE THEREIN, IS NOT MORE THAN 0.4, SAID LIQUID BEING SELECTED FROM THE GROUP CONSISTING OF TETRAHYDRONAPHTHALENE, CYMENE, PINENE, CEDRENE, 0-DICHLOROBENZENE, ALPHA-CHLORNAPHTHALENE AND DECAHYDRONAPHTHALENE. 